1. Field of the Invention
The preset invention relates to a joint structure capable of optimizing a margin of length of an umbilical member, and an industrial robot having the joint structure.
2. Description of the Related Art
In an industrial robot having an upper arm, a forearm rotatably connected to the upper arm, and a wrist element rotatably attached to the forearm, there are two motion patterns, i.e., one pattern in which a rotation center of the forearm is positioned above a straight line connecting rotation centers of the upper arm and the wrist element, and another pattern in which the rotation center of the forearm is positioned below the straight line connecting the rotation centers of the upper arm and the wrist element. Recently, in order to obtain as wide a motion range at the rear side of the robot as possible, a range of rotation angle of the forearm relative to the upper arm is often expanded so that both the above two motion patterns can be used.
As a relevant prior art document, for example, JP 2003-225883 A discloses a configuration in which a plastic outer cable guide 20 is arranged at a cable insert hole 10b having an elongated shape, a plastic inner cable holder 21 for holding a cable 7 is supported in outer cable guide 20 so as to slide in the circumferential direction, and inner cable holder 21, downwardly extending from outer cable guide 20, is positioned at a height corresponding to a connecting portion 8a of a frame 8.
JP 2002-239968 A discloses a configuration having a second arm 14 and a third arm 15, in which a movable first stopper 35 abuts a fixed first stopper 37 when third arm 15 is clockwise rotated, a movable second stopper 36 abuts a fixed second stopper 38 when third arm 15 is counterclockwise rotated, and fixed first stopper 37 and fixed second stopper 38 are arranged on a housing 31 of second arm 14 at positions deviated in both the radial and circumferential directions.
Further, JP 2010-089186 A discloses a robot controller configured to prevent erroneous setting of a movable range of a physical stopper relative to a movable control range of software control, and to set a plurality of movable control ranges within a predetermined movable range of an arm.
In an industrial robot, an umbilical member extending from a robot controller is normally connected to a motor for controlling each axis of the robot. In this case, the length and the position of the (movable) umbilical member about a joint between the upper arm and the forearm are determined so that a stress generated in the umbilical member is within an allowable range even when the upper arm is operated with a relatively wide motion range. Therefore, the umbilical member may widely and outwardly slack in the lateral direction.
On the other hand, the actual robot is not normally operated in the state in which the rotation center of the forearm is positioned below the straight line connecting rotation centers of the upper arm and the wrist element. In such a state, it is desired that the motion range of the forearm be limited so that the length of the umbilical member extending outwardly in the lateral direction is reduced.